1. Field of the Invention
The present invention relates to a distributor type fuel injection pump provided with a pilot injection mechanism, used for supplying fuel to an engine, and more specifically, it relates to an inner cam, distributor type fuel injection pump (VR pump) which causes plungers to make reciprocal movement in the direction of the radius of a rotating distribution member and a distributor type fuel injection pump (VE pump) which distributes fuel by causing a distribution member to make rotating and reciprocal movement.
2. Description of the Related Art
In a VR type distributor type fuel injection pump, as disclosed in First Publication No. S59-110835 of Japanese Patent Application, for instance, a concentric inner cam ring 1 is provided around a fuel distribution rotor 4 (distribution member) and force feed plungers 21 and 22 are provided on the cam surfaces formed on the inside of the inner cam ring 1 via a roller or the like so that the force feed plungers 21 and 22 can make reciprocal movement in the direction of the radius of the fuel distribution rotor 4. In the fuel distribution rotor 4, a pump chamber 2 (compression space) whose volumetric capacity is changed by the force feed plungers 21 and 22, intake holes 51-54 through which fuel is taken into the pump chamber 2 during an intake process, a distribution port 6 which, during a force feed process, delivers fuel that has been pressurized in the pump chamber 2 and overflow ports 71-74, which cut off the fuel delivery, are formed. Also, a ring-like member 7 (control sleeve) is externally fired on the fuel distribution rotor 4, covering the overflow ports 71-74 and by moving this ring-like member in the direction of the axis, the cut off timing during the force feed process can be adjusted to vary the fuel injection quantity.
Now for a VE type distributor type fuel injection pump, as disclosed in First Publication No. S54-102420 of Japanese Patent Application, for instance, a plunger 7 (distribution member) is secured to a cam disk 8 which rotates in synchronization with an engine to cause the plunger 7 to rotate and, at the same time, to make reciprocal movement in correspondence to the cam surface of the cam disk. The from end of the plunger faces a space 10 which constitutes a compression space and in the plunger, a longitudinal groove 11 for taking fuel into the space 10 during the intake process, a distribution longitudinal groove 14 for delivering fuel which as been pressurized in the space 10 during the force feed process and a cut off port 17 for cutting off fuel delivery, are formed. Also, a control sleeve is externally fitted on the plunger 7, covering the cut off port 17 and, by moving this control sleeve in the direction of the axis, cut off timing during the force feed process is adjusted to vary the fuel injection quantity.
In these VR and VE type injection pumps, it is desirable to provide a simple mechanism which satisfies the following requirements without changing the basic structure described above. Namely: 1) since, in the idling range and in the no-load range, the combustion temperature is low, flame-out tends to occur, resulting in white smoke and HC being generated, a pilot injection should be performed prior to the main injection in order to ensure reliable combustion during the main injection; 2) on the other hand, if a pilot injection is performed in the full-load range, the characteristics curve for full-load operation would deteriorate, resulting in reduced torque, generation of black smoke and higher fuel consumption. Consequently, in the full-load range, it is desirable to perform only the main injection without the pilot injection; 3) in the small injection range (low load, low speed range), which particularly requires pilot injection, the pilot injection quantity should be reduced as the main injection quantity decreases.